Add inverse_of: :pipeline for pipeline.builds (#37987)

This appears to reduce the number of queries in pipeline creation of
gitlab-ce's .gitlab-ci.yml by 92

This also means we now need to mock this ci yaml file properly in the
test because otherwise the yaml_errors stay on the object and make all
the pipelines failed.

app/models/ci/pipeline.rb

@@ -14,7 +14,7 @@ module Ci
 
     has_many :stages
     has_many :statuses, class_name: 'CommitStatus', foreign_key: :commit_id, inverse_of: :pipeline
-    has_many :builds, foreign_key: :commit_id
+    has_many :builds, foreign_key: :commit_id, inverse_of: :pipeline
     has_many :trigger_requests, dependent: :destroy, foreign_key: :commit_id # rubocop:disable Cop/ActiveRecordDependent
     has_many :variables, class_name: 'Ci::PipelineVariable'
 

spec/services/ci/process_pipeline_service_spec.rb

@@ -9,6 +9,8 @@ describe Ci::ProcessPipelineService, '#execute' do
   end
 
   before do
+    stub_ci_pipeline_to_return_yaml_file
+
     stub_not_protect_default_branch
 
     project.add_developer(user)